1. Field of the Invention
The present invention relates to a water treatment apparatus, specifically to a rotary flat membrane separation apparatus which is installed in a water treatment system.
2. Description of Related Art
Many membrane separation apparatuses have been applied to practical use as a solid-liquid separation apparatus in the field of water treatment. Among the membrane separation apparatuses, there are a variety of module forms such as a hollow-fiber module, a spiral module, and a flat membrane module, and each module form is applied for its suitable use. A rotary flat membrane module comprises a hollow rotary shaft and rotary flat membrane disks mounted on the rotary shaft and performs filtration while rotating the flat membrane disks. Since the rotary flat membrane module can provide a flux over a membrane surface by rotating the flat membrane disks to prevent a contamination layer from accumulating on the membrane surface, the rotary flat membrane module has an advantage in that it can be operated with a low amount of power, and thus differs from other membrane modules that provide the flux over the membrane surface by circulating subject liquid to be filtrated.
The rotary flat membrane module has a plurality of rotary flat membrane disks mounted on the rotary shaft, and performs filtration while rotating the rotary flat membrane disks. The conventional rotary flat membrane separation apparatus had a problem in that the subject liquid (liquid to be filtrated) between a pair of adjacent rotary flat membranes rotates together with the rotary flat membrane disks as the rotation speed increases, and the flux over the rotary membrane surface cannot be obtained. In order to solve this problem, Japanese Utility Model No. 2023154 suggests a structure in which rotary flat membrane disks mounted on a pair of adjacent rotary shafts are alternately arranged side by side. In this structure, the rotary flat membrane disks mounted on one of the pair of the rotary shafts act as interrupter against the disks mounted on the other of the pair of the rotary shafts, so that the liquid can be prevented from rotating together with the rotary flat membrane disks.
In order to maintain a distance between the adjacent rotary flat membrane disks mounted on the same rotary shaft, a collar is provided between the adjacent rotary flat membrane disks. The diameter of the collar affects the effective membrane area of the rotary flat membrane disks as well as vibration caused by the rotation of the rotary flat membrane disks. In other words, the smaller the diameter of the collar, the larger the effective membrane are of the rotary flat membrane disks, but the rotation rate at filtration cannot be set higher due to the fact that the vibration caused by the rotation of the rotary flat membrane disks becomes larger. Therefore, the adhesion of the contamination layer on the membrane surface progresses, and the flux is small. If the rotation rate is set at a high speed under this state, the rotary flat membrane disks mounted on the adjacent rotary shafts might collide to each other and break. Conversely, the larger the diameter of the collar, the less the vibration caused by the rotation of the rotary flat membrane disks, but the effective membrane area of the rotary flat membrane disks is smaller and a process amount per disk is thus smaller.
The present invention has been developed in view of the above-described circumstances, and has as its object the provision of a rotary flat membrane separation apparatus which overcomes the above-described problems in the conventional technology and which can obtain the effective membrane area as large as possible while preventing the vibration caused by the rotation of the rotary flat membrane disk.
The present invention is established by knowledge that the above-described objects are achieved by setting the ratio between the diameter of the collar and the diameter of the rotary flat membrane disk to be optimum. The present invention is directed to a rotary flat membrane separation apparatus, comprising: a plurality of hollow rotary shafts; a plurality of rotary flat membrane disks mounted on each of the plurality of hollow rotary shafts at regular intervals, the plurality of rotary flat membrane disks mounted on adjacent two of the plurality of hollow rotary shafts being alternately arranged side by side in equal intervals; and a plurality of collars, each of the plurality of collars being arranged between adjacent two of the plurality of rotary flat membrane disks mounted on each of the plurality of hollow rotary shafts, wherein a diameter of the collars is between 0.18-0.34 times a diameter of the rotary flat membrane disks.